RPM Dip at Idle on '05 CS

[Scott C]

I have a phenomenon that occurs under all conditions but is worse when cold on my 2005 CS.When coming to a stop at a speed faster than a crawl, the engine RPMs dip to 400 rpm on the tach and then recovers back to normal speed of about 500.I can hear the engine lug down a bit when it hits 400 but quickly recovers.This issue occurred a few years ago but was "fixed" at the dealer by cleaning the throttle plate.Before digging into the intake, I wanted to see if there was a definitive fix to this issue.Anybody else seen this?

[Loren]

Did you have a look at this TSB?

[Scott C]

Thanks Loren! I'm not sure if this is the case but i will check the DME fault codes and see if anything is stored.

The TSB is not crystal clear but it seems the MAFs may not be outputting proper voltage and cause rough idle. This would explain why it would exhibit rough idle on fairly stiff off-throttle and not from a crawl.

Edited December 19, 2012 by Scott C

[ekstroemtj]

Hi. As i know its a very common issue inside the cayenne community. I had / have the same.

The drop of rpm is a secret issue for me.

We have 2 cayenne s. One has this issue again and again, the other car never had it. This is a miracle for me. We changed coils and plugs, filters. New MAF's and finally in the last weeks a new throttle body. And what you think?! The idle dropping story still continues. So all what i can say, cleaning the throttle body can help you but as you can see in my case, even a new part didnt solve the problem.

[Scott C]

Thanks for sharing your experience. It is not re-assuring that the issue is not easily identified.

I will follow with TSB and see if 1.1V is present so I can rule out MAF.

The throttle plate cleaning appeared to help in my situation in the past so I may pursue that route.

The only other thing I can imagine is a vacuum leak causing this to occur...... Especially when cold.

Good luck!

[ekstroemtj]

I was thinking about this. A leak somewhere but how to find out? How to test if this is the reason?

[Loren]

Find shop or borrow a smoke machine to check for vacuum leaks.

[ekstroemtj]

I went already to porsche explaining the problem but looks like here in the forum guys have more knowledge about this car than all this so called specialists. Last story: i asked to change fuel pump and fuel filter. Answer from shop: cayenne dont have a fuel filter. So far about know how of porsche specialists:-(

[ekstroemtj]

Find shop or borrow a smoke machine to check for vacuum leaks.

Loren i remember you posted a diagramm some time ago which is showing the tubes which could be related to the problem. Do you know where i can find it? Thankx

[Loren]

This?

[ekstroemtj]

This?

Yes thank you, fantastic

[wvicary]

After you cleaning the throttle body reset the adaption value for the throttle body.

[Scott C]

After you cleaning the throttle body reset the adaption value for the throttle body.

Thanks for the tip. Is this process where the vehicle "learns" or is there a value that should be set.

[Loren]

The vehicle learns - so drive like you normally do.

[Scott C]

Thanks Loren!

[ekstroemtj]

Thanks for sharing your experience. It is not re-assuring that the issue is not easily identified.

I will follow with TSB and see if 1.1V is present so I can rule out MAF.

The throttle plate cleaning appeared to help in my situation in the past so I may pursue that route.

The only other thing I can imagine is a vacuum leak causing this to occur...... Especially when cold.

Good luck!

Oh wonder oh wonder, the problem is solved!

What i can say, i had the truck in the shop to replace the fuel pumps. Not because of this idle problem but because of some strange behaviour during full speed driving.

And guess what, THE IDLE DIP PROBLEM IS GONE!!! I am so happy.

What i learned from this, idle dip problems could be caused by fuel pressure problems.

Merry Xmas

[Scott C]

You may be onto something here. Recently the rear fuel pump has started whining rather loudly where it didn't do this in the past.

Certainly fuel pressure has an affect on idle.

I'll look into this and see if the connections are loose like yours.

[ekstroemtj]

You may be onto something here. Recently the rear fuel pump has started whining rather loudly where it didn't do this in the past. Certainly fuel pressure has an affect on idle. I'll look into this and see if the connections are loose like yours.

Was the same with me. Right side noisy . They changed this one and found out, that the main pump on the left was not working.Noise come From right one just because thisOne had to work much more. My advice, check all cable connections or if neccessary change pumps.Dont do it by yourself please.

[paulwu]

On 12/19/2012 at 2:04 AM, ekstroemtj said:

Hi. As i know its a very common issue inside the cayenne community. I had / have the same.

The drop of rpm is a secret issue for me.

We have 2 cayenne s. One has this issue again and again, the other car never had it. This is a miracle for me. We changed coils and plugs, filters. New MAF's and finally in the last weeks a new throttle body. And what you think?! The idle dropping story still continues. So all what i can say, cleaning the throttle body can help you but as you can see in my case, even a new part didnt solve the problem.

 

Hello,

 

Have you found the issue for the drop rpm issue? I have changed everything can think about but still with low rpm stall.  Thanks,

[ekstroemtj]

You have changed both pumps?

[paulwu]

9 minutes ago, ekstroemtj said:

You have changed both pumps?

Yes both fuel pumps have changed!  The vehicle start in cold no problem and no hesitation, only when in warm up then the RPM drops much like low to 440 and then stalls eventually. 

Edited May 20, 2020 by paulwu

[ekstroemtj]

I am not a professional but o guess there is a leak somewhere. Many times with higher temperatures it feels more  and more. To find a leak is difficult. But before hunting for leak take a look at the MAF . If possible Clean them